Growing up, I was obsessed with tornadoes. I daydreamed about them. I watched every TV show about them. I read every book I could find about them – several times. And, in those books, there was only one tornado outbreak that was always mentioned: the Super Outbreak (April 3-4, 1974). It was the grand-daddy of all outbreaks – a veritable monolith of atmospheric violence. Even to this day, its statistics still stun: 2 days, 148 tornadoes, 13 states, 30 violent tornadoes, 6 F5 tornadoes, and 315 dead. It was the benchmark; no other outbreak was even close. Sure, the Palm Sunday Outbreak of 1965 was a doozy, but it was at least a couple notches below the Super Outbreak. It was an outbreak so monstrous that most thought its rival would not come for many lifetimes.
Then, from April 26 to April 28 of 2011, the unthinkable happened: another – even bigger – super outbreak of tornadoes ravaged the Southeast. This time, at least 350 tornadoes occurred across 14 states – including several long-lived, violent tornadoes – killing over 300 people. With its massive number of tornadoes, it easily became the largest tornado outbreak in American history. Of these tornadoes, 15 achieved violent ratings (EF4/EF5), and – perhaps – several more would have had this outbreak occurred in the era of lower ratings standards.
Beyond sheer numbers, though, there are many noteworthy aspects of this outbreak. One was the large number of highly-visible tornadoes (see right). As most storm chasers know, the Southeast isn’t exactly known for visually-impressive tornadoes: fast storm motion, heavy precipitation, high trees, and (of course) darkness often make viewing difficult. Yet, many of the 2011 Super Outbreak tornadoes were highly visible – even at a distance (see 0:40 in this video for an example). I’ve seen several videos of expansive rain-free bases with large tornadoes – almost as if these storms were on the low-precipitation side of the supercell continuum. The only exception seems to be the tornadoes that occurred near the warm front, where lower cloud bases made visibility characteristically tough.
Another fascinating part of this outbreak was the high number of smaller vortices within these tornadoes. The Cullman tornado, in particular, was a vortex bonanza. Horizontal vortices, subvortices – even vortices within vortices – were a common sight. And, of course, who can forget the Tuscaloosa tornado? It contained nearly-ubiquitous “octopus tentacles” – a sight so scary that even the editors of “Weekly World News” would have been powerless to make it more frightening. Additionally, it also featured an invisible, rolling horizontal tube on the front side of the tornado – almost as if the tornado was a giant mower, trimming down the environmental vorticity. Other major-league tornadoes have produced similar vortices, including the Red Rock tornado (4/26/91), the Moore tornado (5/3/99), and the El Reno tornado (5/24/11). These vortices are quite rare, as it seems only the most intense tornadoes produce them.
Finally, these storms displayed an organization in their incipient supercell stage that I’ve never seen. On a given tornado day, most supercells take a good half-hour to an hour to organize themselves into the characteristic pendant shape on radar. These storms, however, wasted no time. Even before they “broke the cap,” these storms appeared to be rotating. More fascinating still, the developing convection in eastern Mississippi (see right) displayed a periodicity between storms that I’ve never seen. In that north-south line, at least 14 developing storms can be identified on radar, with a wavelength ranging from 5 – 10 miles. Interestingly, the more intense the storm in that line became, the greater the distance between it and other storms (as one might expect from storm-scale pressure perturbations).
Are there any other aspects of the outbreak that you find interesting? If you experienced the outbreak(s), what was your experience?